Tropical Ice Reveals Rare Climate Record

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A new and rare ice core record of tropical temperatures
highlights changes in the enfants terribles of world
climate, the El Niño/La Niña–Southern Oscillation.

The climate record comes from Peru's stunning Cordillera Oriental
mountain range, home to Quelccaya, the world's largest
tropical ice cap. Researchers trekked to an altitude of more
than 18,000 feet (5,600 meters) to probe the ice.

The two ice cores (or cylinders of ice) drilled from the
Quelccaya hold 1,800 years of climate history, according to a
study published today (April 4) in the journal Science Express.
Alternating light and dark layers record the wet and dry seasons
at the top of the world — light from snow and dark from dust
during the dry season.

"We have an annual resolution going back 1,300 years, and that's
almost unprecedented," said Ellen Mosley-Thompson, a
paleoclimatologist at Ohio State University and study co-author.
Only a few ice cores from polar regions have longer annual
resolutions, she said. (This resolution means they can see what
the climate was like for each year.)

Big climate patterns

Ice cores draw the attention of climate researchers because the
ratio of oxygen isotopes in the ice acts like a thermometer for
past climate and sea surface temperatures. Isotopes are atoms
with different weights due to different numbers of neutrons in
their nuclei.

One notable climate event in the ice cores is the
Little Ice Age, which chilled these tall mountains from 1520
to 1880. In northern latitudes, the cooling froze New York City's
Harbor and the Thames River in England. In South America, trace
elements such as ammonium and nitrate in the ice indicate the
Amazon was moist, because they reflect increased microbial
activity in the soil, Mosley-Thompson said.

Though most of the moisture for the glacier's snowfall comes from
the east, rising from the Amazon, wet El Niño years
also contribute, Mosley-Thompson said.

In the past 140 years, warm pools of water in the Pacific Ocean
shifted, reflecting changes in the El Niño and the Intertropical
Convergence Zone, the study found. The zone, which is a key
component of global atmospheric circulation, has migrated
northward, according to the ice core record.

"The
Intertropical Convergence Zone is like the hydrologic
equator. It's very critical to who gets water and who doesn't, so
it's very useful to look back in the records and see how it's
moved," Mosley-Thompson told OurAmazingPlanet.

The Quelccaya Ice Cap has shrunk 985 feet (300 meters) since the
researchers first climbed to the glacier in 1983. Plants exposed
by the
retreating tropical ice in 2011 were carbon-dated to 6,298
years ago the study reports.